The invention relates to an apparatus for the transport of workpieces, in particular of suspended, panel-shaped workpieces, such as sheets or plates, with at least one rotationally driven conveyor belt for the workpieces to be laid onto the latter, and with a holding device, past which the conveyor belt is led, the holding device retaining the workpieces on the conveyor belt by means of a magnetic field passing through the conveyor belt and/or by generating a vacuum at suction orifices of the conveyor belt.
The general procedure for conveying workpieces, in particular for the suspended transport of sheets or plates, is, after the sheet has been unwound from a coil, to cut it by means of sheet shears into panels to be further processed. These panels are delivered to a feed conveyor, from which they are received by means of the apparatus initially described. After being transported, the sheets or plates are discarded at desired locations and form stacks for packages on lifting tables. Further processing subsequently takes place, for example, in bending devices or molding presses.
An apparatus in the embodiment initially described became known from DE-C-196 14 741. The set purpose, here, was to allow suspended or supported transport or conveyance of magnetic and nonmagnetic workpieces at high speeds. To this effect, the known teaching provides a combined vacuum/magnet system (VMS) which has at least one magnet arranged adjacent to the transport band and a vacuum duct connected to a vacuum source. This vacuum duct is connected to the suction orifices of the transport band or conveyor belt via suction lines passing through the magnet. The conveyor belt, provided with ferromagnetic inserts, is guided in appropriately shaped guide strips on the magnet. Said conveyor belt is provided, on its side facing the workpieces, with a plurality of successively arranged annular elevations, on which the workpieces bear. Consequently, according to the prior art, one and the same conveyor belt is used for transporting both ferromagnetic and nonferromagnetic workpieces. Moreover, in general, both the vacuum system and the magnet system are in operation, in order to ensure that the workpieces are pressed particularly effectively onto the surface of the transport band. A vacuum is therefore employed even in the conveyance of ferromagnetic workpieces.
The known procedure or the previously published apparatus is often merely a compromise, on the one hand, as regards the ability to suck up workpieces by means of a vacuum and, on the other hand, as regards the outlay in terms of construction. Thus, in the case of the so-called flat seals used according to the prior art, problems may arise on the conveyor belt with respect to leakages which occur. Increased energy consumption for the plant as a whole is therefore to be expected in that case.
In addition, the otherwise known conveyor belts with elevations resembling suction cups (DE-A-30 01 531) are not used at this point, since elevations or suction pockets of this kind may be destroyed by steel plates which are to be transported by means of the conveyor belt.
Moreover, suction losses occur due to the fact that the known conveyor belt with a flat seal cannot readily adapt to dented or otherwise distorted sheet metal plates. Further pressure losses must therefore be expected in the region of a bulge or dent of this kind.
Irrespective of this, an apparatus, working with suction air, for the suspended transport of sheets became known from DE-A-43 42 753. This apparatus has transport bands of finite length which span the transport zone and are arranged transversely to the latter next to and parallel to one another. The transport bands can be driven via common drive and movement means, the movement drive of which is reversible for the purpose of a reciprocating movement of the transport bands and which, in the region in which the sheets are grasped, in each case have a stand-guided slidelike rigid part possessing a sucker means or are connected to such a part. An apparatus for the suspended transport even of nonmagnetizable articles is thereby to be provided.
The technical problem on which the invention is based is to develop an apparatus in the embodiment initially described, in such a way that, along with reduced energy consumption, optimum adaption to the workpieces to be transported is ensured.
To achieve this object, in a generic apparatus of the transport of workpieces, the invention proposes that the holding device have at least one magnetic device with a magnetic conveyor belt and at least one vacuum device separated from this and having a vacuum conveyor belt, the magnetic device and/or the vacuum device in each case being capable of being displaced with their respective conveyor belt relative to a common reference member and (alternately) of being brought into contact with the workpieces to be transported. Within the scope of the invention, the term xe2x80x9calternatelyxe2x80x9d also, of course, includes the possibility of bringing both devices, that is to say the magnetic device and vacuum device, simultaneously into contact with the workpieces.
Furthermore, according to a preferred embodiment, there is provision for jointly connecting the magnetic device and the vacuum device to a profiled holding strip extending in the transport (plane) direction and acting as a reference member, the profiled holding strip having a basic carrier and a displacement carrier, and the magnetic device being flanged to the basic carrier and the vacuum device being flanged to the displacement carrier, or vice versa, said displacement carrier being movable, for this purpose, essentially vertically in relation to the transport (plane) direction. According to an alternative embodiment of the invention, there is provision for the vacuum device to be integrated into the magnetic device designed as a reference member and for said vacuum device to be movable, relative to the usually stationary magnetic device, in the direction of the workpieces. Of course, the normally stationary magnetic device may also be brought, as a whole, into contact with the workpieces, specifically as an as it were vertically adjustable holding device. It also goes without saying that the vacuum device integrated into the magnetic device may also be combined with the above-described device. In other words, within the scope of the invention, it is conceivable to have a holding device which possesses a magnetic device and vacuum device which are connected to a profiled holding strip and, in addition, a vacuum device which is integrated into the magnetic device. Furthermore, there is preferably provision for the magnetic device integrated into the vacuum device to be designed with a U-shaped cross section having a U-base and U-legs, at least two magnetic conveyor belts being led, on the foot side, past the two respective U-legs, while the vacuum device together with the vacuum conveyor belt is arranged in the longitudinal extent between the two magnetic conveyor belts.
By virtue of these measures of the invention, not only is the energy consumption markedly reduced, but, at the same time, optimum adaption to the workpieces to be transported also takes place. It should be emphasized, in this respect, that the apparatus described is suitable both for suspended and for carrying or supporting transport. At all events, it is always ensured that either the magnetic device or the vacuum device are used alternately (or else jointly).
The invention proceeds, in this case, from the current knowledge that, in general, approximately 90% of the transported workpieces are ferromagnetic, and therefore the magnetic device is used predominantly. It is consequently unnecessary to make additional provision for the workpieces to be sucked up. A simple, cost-effective toothed belt can therefore be used as a magnetic conveyor belt. There is no need for special sealing properties because, on the one hand, the magnetic device with the magnetic conveyor belt and, on the other hand, the vacuum device with the vacuum conveyor belt are designed separately. In addition, a vacuum is not required for this mode of operation, and therefore vacuum generation as a whole can be switched off via valves. Moreover, the magnetic conveyor belt can be designed particularly robustly, in order to counteract the, in particular, frictional and abrasive properties of the transported sheets or plates.
Insofar as nonferromagnetic workpieces, for example aluminum sheets, are to be transported, instead of the magnetic device with the magnetic conveyor belt the vacuum device with the vacuum conveyor belt is brought into contact with the workpieces to be transported. This vacuum device and, in particular, the vacuum conveyor belt can therefore be adapted particularly to the problems and requirements arising during vacuum suction.
Thus, the vacuum conveyor belt, usually designed as a toothed belt, is, in general, equipped with suction cups on the front side. In contrast to the prior art according to DEC-196 14 741, these bring about permanent and satisfactory suction of the workpieces to be conveyed. There need be no fear of leakages. This is because even dents or warps in the workpieces are compensated in that the suction cups can be inclined (within certain limits) and therefore adapt to the contour of the sucked-up workpiece. This is not possible with the flat seals provided in the prior art. In addition, for example when aluminum plates are being transported, damage, which is generally to be feared in the case of steel plates, does not occur. This is attributable, in particular, to the fact that aluminum is substantially softer than steel and has nowhere near the same abrasive properties. Moreover, the use of suction cups also makes it possible to suck up workpieces having surfaces which are to a greater or lesser extent soiled. This purpose is served by the internal bosses which are generally provided in the case of suction cups and which, as it were, limit the spring excursion of the suction cup and ensure that the workpiece bears satisfactorily on the latter.
As a result, due to the use of the front-side suction cups, not only is adaption to, for example, dented workpiece surfaces achieved, but even soiled sheets can be sucked up without difficulty. It must be borne in mind, in this case, that the above-mentioned suction cups, when the workpieces come to bear on them, bring about, as it were, a cleaning of the workpiece surface, so that the contact effect between the suction cup and the workpiece or workpiece surface is further improved.
At all events, overall, optimum adaption to the workpieces to be transported is achieved. Although this is at the expense of a generally higher outlay in terms of construction, as compared with the prior art, the costs as a whole are reduced, since energy consumption can be lowered considerably. Moreover, different overall lengths for the magnetic device, on the one hand, and for the vacuum device, on the other hand, can be selected. Cost savings and easy retrofitting are therefore possible. Furthermore, the drive shaft of the vacuum device can remain in the same position, this being achieved by means of a special compensating coupling in the drive head. Moreover, the coefficient of friction of the vacuum conveyor belt is not increased if a load is exerted on the vacuum conveyor belt when workpieces are being transported.
As a result, the known apparatus according to DE-A-43 42 753 operates almost exclusively in an area where unfavorable energy conditions prevail. Insofar as the teaching according to DE-C-196 14 741 is taken into account, the invention affords clear benefits, to the effect that both the vacuum conveyor belt and the magnetic conveyor belt can be adapted optimally to their respective intended uses. Compromises do not have to be reached. Normally, in an operating mode using the magnetic conveyor belt, a vacuum is usually not generated, so that vacuum generation as a whole can be switched off via valves. Of course, in the case of magnetic conveyance, vacuum action may additionally be carried out, should the weight or special nature of the workpieces make this necessary.
By integrating the vacuum device into the (stationary) magnetic device according to the statements in patent claim 7, a particularly compact embodiment having all the above-mentioned advantages is provided. Normally, in this case, and even otherwise, the vacuum conveyor belt together with the vacuum device can preferably be moved into a vacuum conveying plane which is spaced by a predetermined amount from a magnetic conveying plane defined by the magnetic conveyor belt. The vacuum conveyor belt plane and the magnetic conveying plane are usually oriented parallel to one another.
At all events, altogether, optimum adaption to the workpieces to be transported, along with low energy consumption and a compact design, is achieved. The altogether higher outlay in terms of construction, as compared with the prior art, is overcompensated, within the framework of overall cost accounting, due to the fact that, according to the invention, it was possible to lower the energy consumption considerably. Moreover, retrofittings are easily possible. In addition, due to the low mechanical load on the conveyor belts, the maintenance intervals are extended, so that further cost benefits are to be expected.
Other advantageous embodiments are listed below. Thus, the displacement carrier normally has a fastening plate for the vacuum device, said fastening plate sliding along on the basic carrier, and a bush guided vertically in a bore in the basic carrier. This ensures satisfactory vertical guidance of the displacement carrier on the basic carrier. Of course, instead of the vacuum device, the magnetic device may also be connected to the above-mentioned fastening plate. A roller of U-shaped cross section, for riding mounting on a tie rod bearing between the U-legs and on the U-base, is connected to the bush, generally coaxially, that is to say with the same axis, the tie rod being designed to be displaceable in the transport direction and having at least one run-on slope for the vertical movement of the roller and, consequently of the displacement carrier during the actuation of the tie rod. In general, a plurality of magnetic devices and vacuum devices arranged in succession in the transport direction are provided. These may be combined in respective modules, to which further reference will also be made later. The number of above-mentioned run-on slopes depends, of course, on the number of displacement carriers. At all events, altogether, by displacing the tie rod or actuating the latter it is possible to achieve a rapid changeover from magnetic operation to vacuum operation. This is attained simply by moving the displacement carrier or displacement carriers simply or synchronously with the tie rod. In this case, a changeover from xe2x80x9cmagnetic conveyancexe2x80x9d to xe2x80x9cvacuum conveyancexe2x80x9d takes place in less than one second. The riding mounting of the roller on the tie rod ensures, altogether, that the latter is guided satisfactorily. Moreover, the bush guided in the bore may be designed to be mounted eccentrically, in order to allow satisfactory vertical orientation of all the fastening plates and, consequently, vacuum devices.
The magnetic device has, mainly, a hollow profiled strip with main compressed air chambers and a structural unit connected on the transport side and having at least one permanent magnet for generating a permanent magnetic field and at least one electric magnet coil or compensating coil for generating a temporary magnetic field and for compensating the permanent magnetic field. Such a structural unit is described, in principle, for example in DE-C-34 23 482. Reference is made both to this and to German patent application 197 24 634.6-22. The design of the permanent magnet and electric magnet coil is such that the (ferromagnetic) workpieces to be transported are attracted by the permanent magnet. The electric magnet coil serves for compensating this attraction and, as it were, neutralizes the permanent magnetic field and, under certain circumstances, even causes the workpiece to be repelled.
The hollow profiled strip and the above-mentioned structural unit possess, in general, recesses for teeth of the adjacently rotating magnetic conveyor belt. This applies, of course, only when this magnetic conveyor belt is designed as a toothed belt, which is usually the case. The vacuum device has a compressed air guide strip with secondary compressed air chambers and at least one vacuum source with a vacuum generator or vacuum generators, the vacuum source being connected on the delivery side to the compressed air guide strip and on the suction side to the suction orifices. The secondary compressed air chambers are connected to the main compressed air chambers of the magnetic device and are supplied with compressed air by these.
The compressed air guide strip preferably possesses one or more, usually three, secondary compressed air chambers. The vacuum generator is, in general, a Venturi nozzle with a connected vacuum line which is connected to the suction orifices. The procedure may, of course, also be such that, in the vacuum device as a whole, vacuum pumps, blow-up pumps, etc. for a vacuum to act centrally on the suction orifices are provided instead of a Venturi nozzle. However, the advantage of Venturi nozzles is that they make it possible to implement rapid switching frequencies, and, consequently, spot-on discarding and sucking-up of the workpieces to be transported are achieved at a high transport speed. Moreover, Venturi nozzles generally have a sound-insulating effect, particularly where low-frequency sound is concerned.
By using a central permanent magnet and at least one compensating coil surrounding the permanent magnet in the magnetic device, the permanent magnetic field can, as it were, be forced back out of a working gap between the magnetic device and workpieces (with the aid of the compensating coil). Workpieces previously retained magnetically can thereby be discarded at the desired location without difficulty and so as to be aimed at the exact spot. In the case of a vacuum device, discard aimed at the exact spot takes place by corresponding pressure action (instead of the usual suction), as explained in more detail below.
Insofar as the magnetic device is designed with a double-U-shaped cross section having an outer U-armature and an outer armature base and outer armature legs and with an inner U-armature with an inner armature base and inner armature legs, the permanent magnet is conventionally arranged between the two armature bases, the compensating coil being placed in each case between inner and outer armature legs.
In order to move the vacuum conveyor belt or vacuum device into the vacuum conveying plane, the vacuum device normally has a connected adjusting device for essentially vertical movement in the direction of the workpieces and back again. This adjusting device (normally used when the vacuum device is integrated into the magnetic device) is, in general, connected to a guide body or the vacuum device on the head side and to the inner armature base or the magnetic device on the foot side.
In order to act on the suction orifices of the vacuum conveyor belt, the vacuum device may have, in cross section, a guide body with suction bores for the above-mentioned suction orifices in the vacuum conveyor belt. In this case, the suction bores and the suction orifices are normally arranged concentrically on a central axis of the vacuum device. During the rotation of the vacuum conveyor belt, the suction orifices preferably in each case move on a plane of longitudinal extent of a vacuum duct which is connected to the suction bores on the transport side for connecting these to one another. Consequently, within the scope of the invention, it is always ensured that, on the one hand, the suction orifices are continuously in alignment with the vacuum duct and, on the other hand, have maximum overlap with the suction bores when they are led past. Pressure fluctuations are accordingly avoided.
So that the movements of the (integrated) vacuum device together with the vacuum conveyor belt can be compensated in relation to the (stationary) magnetic device, a suction line led laterally past the magnetic device is generally connected to the suction bore in the guide body with movement play. In contrast to the teaching according to DE-C-196 14 741, due to the magnetic device and vacuum device being designed separately, there is no need for the magnetic device to pass through. This should be emphasized expressly. In the simplest case, the suction line may be a flexible hose, but also concentric cubes which engage telescopically one in the other and which are moved one out of the other when the vacuum device is thrown against the workpieces and are inserted one into the other when said device is guided back.
The vacuum conveyor belt may engage, with rear sealing lips, into sealing gaps forming between centering jaws of the central guide body which are located on both sides. For this purpose, the guide body is conventionally designed symmetrically in relation to the already above-mentioned central axis (of the vacuum device) and has centering jaws located on both sides, so as to form an essentially U-shaped cross-sectional profile.
A particularly compact embodiment with regard to the vacuum device integrated into the magnetic device is defined in that the guide body together with the centering jaws has a transverse extent adapted to the width of the vacuum conveyor belt, the guide body, centering jaws and vacuum conveyor belt being inserted with lateral play into the inner U-armature. According to a preferred embodiment of the invention, the vacuum conveyor belt is normally one such as is described in German patent application 197 31 902.5-22, to which express reference is made.
Furthermore, the procedure is, in general, such that the vacuum device has two valves, each with two positions, one valve being designed for applying pressure to the vacuum source, and the other valve, bypassing the vacuum source, being designed for applying pressure to the suction orifices. Idle times between sucking up and discarding the transported workpiece are thereby successfully avoided. This is because, while one valve is still being opened in order to apply pressure to the vacuum source, and consequently the vacuum source acts with a vacuum on the suction orifices on the suction side, the other valve bridging the vacuum source can already be opened. Accordingly, a seamless transition from suction to repulsion (by means of the excess pressure built up by the bridging valve) can be implemented. This is of considerable importance, particularly in view of the short cycle times which are customary nowadays.
Finally, according to a further proposal of the invention, there is provision for connecting the vacuum duct in the plane of longitudinal extent or longitudinal plane, in individual sections each with two or more suction bores with connected suction lines, to a vacuum source in each case, so as to form respective suction modules. In this case, at least one vacuum limiting valve (VBV), vacuum-switched parallel to the suction bores or suction lines, is usually provided. In order to limit the vacuum, this vacuum limiting valve conventionally opens at a predetermined vacuum threshold value in the vacuum duct or the suction lines or in the vacuum line. In particular, for this purpose, there is preferably provision for the vacuum limiting valve to have a vacuum chamber which is connected to the suction lines or to the common vacuum line and which, spring-assisted, is shut off relative to atmospheric pressure by means of a valve disk connected to a valve tappet and closing an air inlet orifice.
The invention thereby takes account of the fact that, with an increasing number of closed suction orifices or suction cups of the vacuum conveyor belt, the vacuum occurring in the vacuum duct or the vacuum system as a whole rises to unacceptable values. The result of this is that the vacuum conveyor belt is ultimately sucked onto the vacuum device and in this case, in particular, the guide body. The friction between the guide body and vacuum conveyor belt is thereby increased, to such an extent that operating impairments, at the very least sluggish running of the vacuum conveyor belt, are to be feared. Moreover, the energy consumption for driving the vacuum conveyor belt thereby rises disproportionately.
These problems are countered, according to the invention, by the vacuum limiting valve (VBV) which is switched parallel to the suction lines or the common vacuum line and, consequently, to the vacuum source. Ultimately, it is important merely to provide this vacuum limiting valve at any location in the vacuum system. This is because this valve ensures, as a result, that, beyond a specific vacuum threshold value in the vacuum duct, the connected suction bores and the suction lines or the common vacuum line, supply air can enter the above-mentioned system. This takes place in such a way that, beyond a specific vacuum, the valve disk is lifted off from the supply air orifice counter to spring force, so that outside air or supply air can penetrate into the vacuum chamber. Consequently, the vacuum in the vacuum duct, the suction lines, the common vacuum line and, of course, also in the suction bores leading to the suction cups and in the suction orifices in the vacuum conveyor belt decreases, with the result that the vacuum conveyor belt is sucked up to a lesser extent. The friction between the vacuum conveyor belt and guide body simultaneously decreases.
In conclusion, the drive power of the vacuum conveyor belt can be reduced considerably. Moreover, by appropriately setting the vacuum limiting valve, a constant and, at the same time, variably adjustable suction force may be employed. In this way, wear between the conveyor belt and guide body decreases and the transport of sucked-up workpieces, in particular sheets or plates, becomes altogether free of jolts. Quiet running of all movable parts is achieved at the same time. By working with a reduced suction vacuum, satisfactory and uniform release of the workpieces transported in suspension on the vacuum conveyor belt is obtained. Moreover, the time constant for sucking up and/or discarding sheets or plates is extremely short. As a result of this, the transport speeds can be increased and the cycle times reduced. This allows an altogether higher throughput of transported workpieces, as compared with an apparatus without a vacuum limiting valve. Finally, the reduction in drive power is accompanied by lower energy consumption and, furthermore, the noise level is markedly lowered. This is plainly and simply because, due to the reduced pressures (sucking up and discarding pressure), the associated noises are also reduced. Furthermore, an indirect effect which emerges is that the frictional forces between the vacuum conveyor belt and guide body are reduced, thus minimizing frictional and, possibly, blockage noises.